def trim(s):
    while len(s) >0  and s[:1]==' ':
        s = s[1:]
    while len(s) >0 and s[-1:]==' ':
        s = s[:-1]
    return s

# 测试:aaa
if trim('hello  ') != 'hello':
    print('测试失败1!')
elif trim('  hello') != 'hello':
    print('测试失败!')
elif trim('  hello  ') != 'hello':
    print('测试失败3!')
elif trim('  hello  world  ') != 'hello  world':
    print('测试失败4!')
elif trim('') != '':
    print('测试失败5!')
elif trim('    ') != '':
    print('测试失败6!')
else:
    print('测试成功7!')